8020291: j.u.c.CompletionStage

8020435: CompletableFuture/Basic.java fails on single core machine
Reviewed-by: chegar, psandoz
Contributed-by: Doug Lea <dl@cs.oswego.edu>

2 files changed, 1543 insertions, 1078 deletions

diff --git a/src/share/classes/java/util/concurrent/CompletableFuture.java b/src/share/classes/java/util/concurrent/CompletableFuture.java
index 7926f2e63b..5e2fb134fc 100644
--- a/src/share/classes/java/util/concurrent/CompletableFuture.java
+++ b/src/share/classes/java/util/concurrent/CompletableFuture.java
@@ -48,13 +48,16 @@ import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.CancellationException;
+import java.util.concurrent.CompletionException;
+import java.util.concurrent.CompletionStage;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.locks.LockSupport;
 
 /**
  * A {@link Future} that may be explicitly completed (setting its
- * value and status), and may include dependent functions and actions
- * that trigger upon its completion.
+ * value and status), and may be used as a {@link CompletionStage},
+ * supporting dependent functions and actions that trigger upon its
+ * completion.
  *
  * <p>When two or more threads attempt to
  * {@link #complete complete},
@@ -62,64 +65,50 @@ import java.util.concurrent.locks.LockSupport;
  * {@link #cancel cancel}
  * a CompletableFuture, only one of them succeeds.
  *
- * <p>Methods are available for adding dependents based on
- * user-provided Functions, Consumers, or Runnables. The appropriate
- * form to use depends on whether actions require arguments and/or
- * produce results.  Completion of a dependent action will trigger the
- * completion of another CompletableFuture.  Actions may also be
- * triggered after either or both the current and another
- * CompletableFuture complete.  Multiple CompletableFutures may also
- * be grouped as one using {@link #anyOf(CompletableFuture...)} and
- * {@link #allOf(CompletableFuture...)}.
+ * <p>In addition to these and related methods for directly
+ * manipulating status and results, CompletableFuture implements
+ * interface {@link CompletionStage} with the following policies: <ul>
  *
- * <p>CompletableFutures themselves do not execute asynchronously.
- * However, actions supplied for dependent completions of another
- * CompletableFuture may do so, depending on whether they are provided
- * via one of the <em>async</em> methods (that is, methods with names
- * of the form <tt><var>xxx</var>Async</tt>).  The <em>async</em>
- * methods provide a way to commence asynchronous processing of an
- * action using either a given {@link Executor} or by default the
- * {@link ForkJoinPool#commonPool()}. To simplify monitoring,
+ * <li>Actions supplied for dependent completions of
+ * <em>non-async</em> methods may be performed by the thread that
+ * completes the current CompletableFuture, or by any other caller of
+ * a completion method.</li>
+ *
+ * <li>All <em>async</em> methods without an explicit Executor
+ * argument are performed using the {@link ForkJoinPool#commonPool()}
+ * (unless it does not support a parallelism level of at least two, in
+ * which case, a new Thread is used). To simplify monitoring,
  * debugging, and tracking, all generated asynchronous tasks are
- * instances of the marker interface {@link AsynchronousCompletionTask}.
+ * instances of the marker interface {@link
+ * AsynchronousCompletionTask}. </li>
  *
- * <p>Actions supplied for dependent completions of <em>non-async</em>
- * methods may be performed by the thread that completes the current
- * CompletableFuture, or by any other caller of these methods.  There
- * are no guarantees about the order of processing completions unless
- * constrained by these methods.
+ * <li>All CompletionStage methods are implemented independently of
+ * other public methods, so the behavior of one method is not impacted
+ * by overrides of others in subclasses.  </li> </ul>
  *
- * <p>Since (unlike {@link FutureTask}) this class has no direct
- * control over the computation that causes it to be completed,
- * cancellation is treated as just another form of exceptional completion.
- * Method {@link #cancel cancel} has the same effect as
- * {@code completeExceptionally(new CancellationException())}.
+ * <p>CompletableFuture also implements {@link Future} with the following
+ * policies: <ul>
  *
- * <p>Upon exceptional completion (including cancellation), or when a
- * completion entails an additional computation which terminates
- * abruptly with an (unchecked) exception or error, then all of their
- * dependent completions (and their dependents in turn) generally act
- * as {@code completeExceptionally} with a {@link CompletionException}
- * holding that exception as its cause.  However, the {@link
- * #exceptionally exceptionally} and {@link #handle handle}
- * completions <em>are</em> able to handle exceptional completions of
- * the CompletableFutures they depend on.
+ * <li>Since (unlike {@link FutureTask}) this class has no direct
+ * control over the computation that causes it to be completed,
+ * cancellation is treated as just another form of exceptional
+ * completion.  Method {@link #cancel cancel} has the same effect as
+ * {@code completeExceptionally(new CancellationException())}. Method
+ * {@link #isCompletedExceptionally} can be used to determine if a
+ * CompletableFuture completed in any exceptional fashion.</li>
  *
- * <p>In case of exceptional completion with a CompletionException,
+ * <li>In case of exceptional completion with a CompletionException,
  * methods {@link #get()} and {@link #get(long, TimeUnit)} throw an
  * {@link ExecutionException} with the same cause as held in the
- * corresponding CompletionException.  However, in these cases,
- * methods {@link #join()} and {@link #getNow} throw the
- * CompletionException, which simplifies usage.
- *
- * <p>Arguments used to pass a completion result (that is, for parameters
- * of type {@code T}) may be null, but passing a null value for any other
- * parameter will result in a {@link NullPointerException} being thrown.
+ * corresponding CompletionException.  To simplify usage in most
+ * contexts, this class also defines methods {@link #join()} and
+ * {@link #getNow} that instead throw the CompletionException directly
+ * in these cases.</li> </ul>
  *
  * @author Doug Lea
  * @since 1.8
  */
-public class CompletableFuture<T> implements Future<T> {
+public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
 
     /*
      * Overview:
@@ -438,6 +427,19 @@ public class CompletableFuture<T> implements Future<T> {
         public final void run() { exec(); }
     }
 
+    /**
+     * Starts the given async task using the given executor, unless
+     * the executor is ForkJoinPool.commonPool and it has been
+     * disabled, in which case starts a new thread.
+     */
+    static void execAsync(Executor e, Async r) {
+        if (e == ForkJoinPool.commonPool() &&
+            ForkJoinPool.getCommonPoolParallelism() <= 1)
+            new Thread(r).start();
+        else
+            e.execute(r);
+    }
+
     static final class AsyncRun extends Async {
         final Runnable fn;
         final CompletableFuture<Void> dst;
@@ -538,13 +540,13 @@ public class CompletableFuture<T> implements Future<T> {
     static final class AsyncAccept<T> extends Async {
         final T arg;
         final Consumer<? super T> fn;
-        final CompletableFuture<Void> dst;
+        final CompletableFuture<?> dst;
         AsyncAccept(T arg, Consumer<? super T> fn,
-                    CompletableFuture<Void> dst) {
+                    CompletableFuture<?> dst) {
             this.arg = arg; this.fn = fn; this.dst = dst;
         }
         public final boolean exec() {
-            CompletableFuture<Void> d; Throwable ex;
+            CompletableFuture<?> d; Throwable ex;
             if ((d = this.dst) != null && d.result == null) {
                 try {
                     fn.accept(arg);
@@ -563,14 +565,14 @@ public class CompletableFuture<T> implements Future<T> {
         final T arg1;
         final U arg2;
         final BiConsumer<? super T,? super U> fn;
-        final CompletableFuture<Void> dst;
+        final CompletableFuture<?> dst;
         AsyncAcceptBoth(T arg1, U arg2,
                         BiConsumer<? super T,? super U> fn,
-                        CompletableFuture<Void> dst) {
+                        CompletableFuture<?> dst) {
             this.arg1 = arg1; this.arg2 = arg2; this.fn = fn; this.dst = dst;
         }
         public final boolean exec() {
-            CompletableFuture<Void> d; Throwable ex;
+            CompletableFuture<?> d; Throwable ex;
             if ((d = this.dst) != null && d.result == null) {
                 try {
                     fn.accept(arg1, arg2);
@@ -587,10 +589,10 @@ public class CompletableFuture<T> implements Future<T> {
 
     static final class AsyncCompose<T,U> extends Async {
         final T arg;
-        final Function<? super T, CompletableFuture<U>> fn;
+        final Function<? super T, ? extends CompletionStage<U>> fn;
         final CompletableFuture<U> dst;
         AsyncCompose(T arg,
-                     Function<? super T, CompletableFuture<U>> fn,
+                     Function<? super T, ? extends CompletionStage<U>> fn,
                      CompletableFuture<U> dst) {
             this.arg = arg; this.fn = fn; this.dst = dst;
         }
@@ -598,7 +600,8 @@ public class CompletableFuture<T> implements Future<T> {
             CompletableFuture<U> d, fr; U u; Throwable ex;
             if ((d = this.dst) != null && d.result == null) {
                 try {
-                    fr = fn.apply(arg);
+                    CompletionStage<U> cs = fn.apply(arg);
+                    fr = (cs == null) ? null : cs.toCompletableFuture();
                     ex = (fr == null) ? new NullPointerException() : null;
                 } catch (Throwable rex) {
                     ex = rex;
@@ -626,6 +629,33 @@ public class CompletableFuture<T> implements Future<T> {
         private static final long serialVersionUID = 5232453952276885070L;
     }
 
+    static final class AsyncWhenComplete<T> extends Async {
+        final T arg1;
+        final Throwable arg2;
+        final BiConsumer<? super T,? super Throwable> fn;
+        final CompletableFuture<T> dst;
+        AsyncWhenComplete(T arg1, Throwable arg2,
+                          BiConsumer<? super T,? super Throwable> fn,
+                          CompletableFuture<T> dst) {
+            this.arg1 = arg1; this.arg2 = arg2; this.fn = fn; this.dst = dst;
+        }
+        public final boolean exec() {
+            CompletableFuture<T> d;
+            if ((d = this.dst) != null && d.result == null) {
+                Throwable ex = arg2;
+                try {
+                    fn.accept(arg1, ex);
+                } catch (Throwable rex) {
+                    if (ex == null)
+                        ex = rex;
+                }
+                d.internalComplete(arg1, ex);
+            }
+            return true;
+        }
+        private static final long serialVersionUID = 5232453952276885070L;
+    }
+
     /* ------------- Completions -------------- */
 
     /**
@@ -680,7 +710,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncApply<T,U>(t, fn, dst));
+                            execAsync(e, new AsyncApply<T,U>(t, fn, dst));
                         else
                             u = fn.apply(t);
                     } catch (Throwable rex) {
@@ -697,11 +727,11 @@ public class CompletableFuture<T> implements Future<T> {
     static final class ThenAccept<T> extends Completion {
         final CompletableFuture<? extends T> src;
         final Consumer<? super T> fn;
-        final CompletableFuture<Void> dst;
+        final CompletableFuture<?> dst;
         final Executor executor;
         ThenAccept(CompletableFuture<? extends T> src,
                    Consumer<? super T> fn,
-                   CompletableFuture<Void> dst,
+                   CompletableFuture<?> dst,
                    Executor executor) {
             this.src = src; this.fn = fn; this.dst = dst;
             this.executor = executor;
@@ -709,7 +739,7 @@ public class CompletableFuture<T> implements Future<T> {
         public final void run() {
             final CompletableFuture<? extends T> a;
             final Consumer<? super T> fn;
-            final CompletableFuture<Void> dst;
+            final CompletableFuture<?> dst;
             Object r; T t; Throwable ex;
             if ((dst = this.dst) != null &&
                 (fn = this.fn) != null &&
@@ -729,7 +759,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncAccept<T>(t, fn, dst));
+                            execAsync(e, new AsyncAccept<T>(t, fn, dst));
                         else
                             fn.accept(t);
                     } catch (Throwable rex) {
@@ -773,7 +803,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncRun(fn, dst));
+                            execAsync(e, new AsyncRun(fn, dst));
                         else
                             fn.run();
                     } catch (Throwable rex) {
@@ -839,7 +869,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncCombine<T,U,V>(t, u, fn, dst));
+                            execAsync(e, new AsyncCombine<T,U,V>(t, u, fn, dst));
                         else
                             v = fn.apply(t, u);
                     } catch (Throwable rex) {
@@ -904,7 +934,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncAcceptBoth<T,U>(t, u, fn, dst));
+                            execAsync(e, new AsyncAcceptBoth<T,U>(t, u, fn, dst));
                         else
                             fn.accept(t, u);
                     } catch (Throwable rex) {
@@ -956,7 +986,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncRun(fn, dst));
+                            execAsync(e, new AsyncRun(fn, dst));
                         else
                             fn.run();
                     } catch (Throwable rex) {
@@ -1042,7 +1072,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncApply<T,U>(t, fn, dst));
+                            execAsync(e, new AsyncApply<T,U>(t, fn, dst));
                         else
                             u = fn.apply(t);
                     } catch (Throwable rex) {
@@ -1095,7 +1125,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncAccept<T>(t, fn, dst));
+                            execAsync(e, new AsyncAccept<T>(t, fn, dst));
                         else
                             fn.accept(t);
                     } catch (Throwable rex) {
@@ -1143,7 +1173,7 @@ public class CompletableFuture<T> implements Future<T> {
                 if (ex == null) {
                     try {
                         if (e != null)
-                            e.execute(new AsyncRun(fn, dst));
+                            execAsync(e, new AsyncRun(fn, dst));
                         else
                             fn.run();
                     } catch (Throwable rex) {
@@ -1226,6 +1256,54 @@ public class CompletableFuture<T> implements Future<T> {
         private static final long serialVersionUID = 5232453952276885070L;
     }
 
+    static final class WhenCompleteCompletion<T> extends Completion {
+        final CompletableFuture<? extends T> src;
+        final BiConsumer<? super T, ? super Throwable> fn;
+        final CompletableFuture<T> dst;
+        final Executor executor;
+        WhenCompleteCompletion(CompletableFuture<? extends T> src,
+                                  BiConsumer<? super T, ? super Throwable> fn,
+                                  CompletableFuture<T> dst,
+                                  Executor executor) {
+            this.src = src; this.fn = fn; this.dst = dst;
+            this.executor = executor;
+        }
+        public final void run() {
+            final CompletableFuture<? extends T> a;
+            final BiConsumer<? super T, ? super Throwable> fn;
+            final CompletableFuture<T> dst;
+            Object r; T t; Throwable ex;
+            if ((dst = this.dst) != null &&
+                (fn = this.fn) != null &&
+                (a = this.src) != null &&
+                (r = a.result) != null &&
+                compareAndSet(0, 1)) {
+                if (r instanceof AltResult) {
+                    ex = ((AltResult)r).ex;
+                    t = null;
+                }
+                else {
+                    ex = null;
+                    @SuppressWarnings("unchecked") T tr = (T) r;
+                    t = tr;
+                }
+                Executor e = executor;
+                Throwable dx = null;
+                try {
+                    if (e != null)
+                        execAsync(e, new AsyncWhenComplete<T>(t, ex, fn, dst));
+                    else
+                        fn.accept(t, ex);
+                } catch (Throwable rex) {
+                    dx = rex;
+                }
+                if (e == null || dx != null)
+                    dst.internalComplete(t, ex != null ? ex : dx);
+            }
+        }
+        private static final long serialVersionUID = 5232453952276885070L;
+    }
+
     static final class ThenCopy<T> extends Completion {
         final CompletableFuture<?> src;
         final CompletableFuture<T> dst;
@@ -1286,10 +1364,13 @@ public class CompletableFuture<T> implements Future<T> {
         final CompletableFuture<? extends T> src;
         final BiFunction<? super T, Throwable, ? extends U> fn;
         final CompletableFuture<U> dst;
+        final Executor executor;
         HandleCompletion(CompletableFuture<? extends T> src,
                          BiFunction<? super T, Throwable, ? extends U> fn,
-                         CompletableFuture<U> dst) {
+                         CompletableFuture<U> dst,
+                          Executor executor) {
             this.src = src; this.fn = fn; this.dst = dst;
+            this.executor = executor;
         }
         public final void run() {
             final CompletableFuture<? extends T> a;
@@ -1310,13 +1391,19 @@ public class CompletableFuture<T> implements Future<T> {
                     @SuppressWarnings("unchecked") T tr = (T) r;
                     t = tr;
                 }
-                U u = null; Throwable dx = null;
+                Executor e = executor;
+                U u = null;
+                Throwable dx = null;
                 try {
-                    u = fn.apply(t, ex);
+                    if (e != null)
+                        execAsync(e, new AsyncCombine<T,Throwable,U>(t, ex, fn, dst));
+                    else
+                        u = fn.apply(t, ex);
                 } catch (Throwable rex) {
                     dx = rex;
                 }
-                dst.internalComplete(u, dx);
+                if (e == null || dx != null)
+                    dst.internalComplete(u, dx);
             }
         }
         private static final long serialVersionUID = 5232453952276885070L;
@@ -1324,11 +1411,11 @@ public class CompletableFuture<T> implements Future<T> {
 
     static final class ThenCompose<T,U> extends Completion {
         final CompletableFuture<? extends T> src;
-        final Function<? super T, CompletableFuture<U>> fn;
+        final Function<? super T, ? extends CompletionStage<U>> fn;
         final CompletableFuture<U> dst;
         final Executor executor;
         ThenCompose(CompletableFuture<? extends T> src,
-                    Function<? super T, CompletableFuture<U>> fn,
+                    Function<? super T, ? extends CompletionStage<U>> fn,
                     CompletableFuture<U> dst,
                     Executor executor) {
             this.src = src; this.fn = fn; this.dst = dst;
@@ -1336,7 +1423,7 @@ public class CompletableFuture<T> implements Future<T> {
         }
         public final void run() {
             final CompletableFuture<? extends T> a;
-            final Function<? super T, CompletableFuture<U>> fn;
+            final Function<? super T, ? extends CompletionStage<U>> fn;
             final CompletableFuture<U> dst;
             Object r; T t; Throwable ex; Executor e;
             if ((dst = this.dst) != null &&
@@ -1358,10 +1445,12 @@ public class CompletableFuture<T> implements Future<T> {
                 boolean complete = false;
                 if (ex == null) {
                     if ((e = executor) != null)
-                        e.execute(new AsyncCompose<T,U>(t, fn, dst));
+                        execAsync(e, new AsyncCompose<T,U>(t, fn, dst));
                     else {
                         try {
-                            if ((c = fn.apply(t)) == null)
+                            CompletionStage<U> cs = fn.apply(t);
+                            c = (cs == null) ? null : cs.toCompletableFuture();
+                            if (c == null)
                                 ex = new NullPointerException();
                         } catch (Throwable rex) {
                             ex = rex;
@@ -1401,322 +1490,7 @@ public class CompletableFuture<T> implements Future<T> {
         private static final long serialVersionUID = 5232453952276885070L;
     }
 
-    // public methods
-
-    /**
-     * Creates a new incomplete CompletableFuture.
-     */
-    public CompletableFuture() {
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * by a task running in the {@link ForkJoinPool#commonPool()} with
-     * the value obtained by calling the given Supplier.
-     *
-     * @param supplier a function returning the value to be used
-     * to complete the returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier) {
-        if (supplier == null) throw new NullPointerException();
-        CompletableFuture<U> f = new CompletableFuture<U>();
-        ForkJoinPool.commonPool().
-            execute((ForkJoinTask<?>)new AsyncSupply<U>(supplier, f));
-        return f;
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * by a task running in the given executor with the value obtained
-     * by calling the given Supplier.
-     *
-     * @param supplier a function returning the value to be used
-     * to complete the returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier,
-                                                       Executor executor) {
-        if (executor == null || supplier == null)
-            throw new NullPointerException();
-        CompletableFuture<U> f = new CompletableFuture<U>();
-        executor.execute(new AsyncSupply<U>(supplier, f));
-        return f;
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * by a task running in the {@link ForkJoinPool#commonPool()} after
-     * it runs the given action.
-     *
-     * @param runnable the action to run before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public static CompletableFuture<Void> runAsync(Runnable runnable) {
-        if (runnable == null) throw new NullPointerException();
-        CompletableFuture<Void> f = new CompletableFuture<Void>();
-        ForkJoinPool.commonPool().
-            execute((ForkJoinTask<?>)new AsyncRun(runnable, f));
-        return f;
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * by a task running in the given executor after it runs the given
-     * action.
-     *
-     * @param runnable the action to run before completing the
-     * returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public static CompletableFuture<Void> runAsync(Runnable runnable,
-                                                   Executor executor) {
-        if (executor == null || runnable == null)
-            throw new NullPointerException();
-        CompletableFuture<Void> f = new CompletableFuture<Void>();
-        executor.execute(new AsyncRun(runnable, f));
-        return f;
-    }
-
-    /**
-     * Returns a new CompletableFuture that is already completed with
-     * the given value.
-     *
-     * @param value the value
-     * @return the completed CompletableFuture
-     */
-    public static <U> CompletableFuture<U> completedFuture(U value) {
-        CompletableFuture<U> f = new CompletableFuture<U>();
-        f.result = (value == null) ? NIL : value;
-        return f;
-    }
-
-    /**
-     * Returns {@code true} if completed in any fashion: normally,
-     * exceptionally, or via cancellation.
-     *
-     * @return {@code true} if completed
-     */
-    public boolean isDone() {
-        return result != null;
-    }
-
-    /**
-     * Waits if necessary for this future to complete, and then
-     * returns its result.
-     *
-     * @return the result value
-     * @throws CancellationException if this future was cancelled
-     * @throws ExecutionException if this future completed exceptionally
-     * @throws InterruptedException if the current thread was interrupted
-     * while waiting
-     */
-    public T get() throws InterruptedException, ExecutionException {
-        Object r; Throwable ex, cause;
-        if ((r = result) == null && (r = waitingGet(true)) == null)
-            throw new InterruptedException();
-        if (!(r instanceof AltResult)) {
-            @SuppressWarnings("unchecked") T tr = (T) r;
-            return tr;
-        }
-        if ((ex = ((AltResult)r).ex) == null)
-            return null;
-        if (ex instanceof CancellationException)
-            throw (CancellationException)ex;
-        if ((ex instanceof CompletionException) &&
-            (cause = ex.getCause()) != null)
-            ex = cause;
-        throw new ExecutionException(ex);
-    }
-
-    /**
-     * Waits if necessary for at most the given time for this future
-     * to complete, and then returns its result, if available.
-     *
-     * @param timeout the maximum time to wait
-     * @param unit the time unit of the timeout argument
-     * @return the result value
-     * @throws CancellationException if this future was cancelled
-     * @throws ExecutionException if this future completed exceptionally
-     * @throws InterruptedException if the current thread was interrupted
-     * while waiting
-     * @throws TimeoutException if the wait timed out
-     */
-    public T get(long timeout, TimeUnit unit)
-        throws InterruptedException, ExecutionException, TimeoutException {
-        Object r; Throwable ex, cause;
-        long nanos = unit.toNanos(timeout);
-        if (Thread.interrupted())
-            throw new InterruptedException();
-        if ((r = result) == null)
-            r = timedAwaitDone(nanos);
-        if (!(r instanceof AltResult)) {
-            @SuppressWarnings("unchecked") T tr = (T) r;
-            return tr;
-        }
-        if ((ex = ((AltResult)r).ex) == null)
-            return null;
-        if (ex instanceof CancellationException)
-            throw (CancellationException)ex;
-        if ((ex instanceof CompletionException) &&
-            (cause = ex.getCause()) != null)
-            ex = cause;
-        throw new ExecutionException(ex);
-    }
-
-    /**
-     * Returns the result value when complete, or throws an
-     * (unchecked) exception if completed exceptionally. To better
-     * conform with the use of common functional forms, if a
-     * computation involved in the completion of this
-     * CompletableFuture threw an exception, this method throws an
-     * (unchecked) {@link CompletionException} with the underlying
-     * exception as its cause.
-     *
-     * @return the result value
-     * @throws CancellationException if the computation was cancelled
-     * @throws CompletionException if this future completed
-     * exceptionally or a completion computation threw an exception
-     */
-    public T join() {
-        Object r; Throwable ex;
-        if ((r = result) == null)
-            r = waitingGet(false);
-        if (!(r instanceof AltResult)) {
-            @SuppressWarnings("unchecked") T tr = (T) r;
-            return tr;
-        }
-        if ((ex = ((AltResult)r).ex) == null)
-            return null;
-        if (ex instanceof CancellationException)
-            throw (CancellationException)ex;
-        if (ex instanceof CompletionException)
-            throw (CompletionException)ex;
-        throw new CompletionException(ex);
-    }
-
-    /**
-     * Returns the result value (or throws any encountered exception)
-     * if completed, else returns the given valueIfAbsent.
-     *
-     * @param valueIfAbsent the value to return if not completed
-     * @return the result value, if completed, else the given valueIfAbsent
-     * @throws CancellationException if the computation was cancelled
-     * @throws CompletionException if this future completed
-     * exceptionally or a completion computation threw an exception
-     */
-    public T getNow(T valueIfAbsent) {
-        Object r; Throwable ex;
-        if ((r = result) == null)
-            return valueIfAbsent;
-        if (!(r instanceof AltResult)) {
-            @SuppressWarnings("unchecked") T tr = (T) r;
-            return tr;
-        }
-        if ((ex = ((AltResult)r).ex) == null)
-            return null;
-        if (ex instanceof CancellationException)
-            throw (CancellationException)ex;
-        if (ex instanceof CompletionException)
-            throw (CompletionException)ex;
-        throw new CompletionException(ex);
-    }
-
-    /**
-     * If not already completed, sets the value returned by {@link
-     * #get()} and related methods to the given value.
-     *
-     * @param value the result value
-     * @return {@code true} if this invocation caused this CompletableFuture
-     * to transition to a completed state, else {@code false}
-     */
-    public boolean complete(T value) {
-        boolean triggered = result == null &&
-            UNSAFE.compareAndSwapObject(this, RESULT, null,
-                                        value == null ? NIL : value);
-        postComplete();
-        return triggered;
-    }
-
-    /**
-     * If not already completed, causes invocations of {@link #get()}
-     * and related methods to throw the given exception.
-     *
-     * @param ex the exception
-     * @return {@code true} if this invocation caused this CompletableFuture
-     * to transition to a completed state, else {@code false}
-     */
-    public boolean completeExceptionally(Throwable ex) {
-        if (ex == null) throw new NullPointerException();
-        boolean triggered = result == null &&
-            UNSAFE.compareAndSwapObject(this, RESULT, null, new AltResult(ex));
-        postComplete();
-        return triggered;
-    }
-
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when this CompletableFuture completes, with the result of the
-     * given function of this CompletableFuture's result.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied function throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<U> thenApply(Function<? super T,? extends U> fn) {
-        return doThenApply(fn, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when this CompletableFuture completes, with the result of the
-     * given function of this CompletableFuture's result from a
-     * task running in the {@link ForkJoinPool#commonPool()}.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied function throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<U> thenApplyAsync
-        (Function<? super T,? extends U> fn) {
-        return doThenApply(fn, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when this CompletableFuture completes, with the result of the
-     * given function of this CompletableFuture's result from a
-     * task running in the given executor.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied function throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<U> thenApplyAsync
-        (Function<? super T,? extends U> fn,
-         Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doThenApply(fn, executor);
-    }
+    // Implementations of stage methods with (plain, async, Executor) forms
 
     private <U> CompletableFuture<U> doThenApply
         (Function<? super T,? extends U> fn,
@@ -1749,7 +1523,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncApply<T,U>(t, fn, dst));
+                        execAsync(e, new AsyncApply<T,U>(t, fn, dst));
                     else
                         u = fn.apply(t);
                 } catch (Throwable rex) {
@@ -1763,65 +1537,6 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when this CompletableFuture completes, after performing the given
-     * action with this CompletableFuture's result.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied action throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> thenAccept(Consumer<? super T> block) {
-        return doThenAccept(block, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when this CompletableFuture completes, after performing the given
-     * action with this CompletableFuture's result from a task running
-     * in the {@link ForkJoinPool#commonPool()}.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied action throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> thenAcceptAsync(Consumer<? super T> block) {
-        return doThenAccept(block, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when this CompletableFuture completes, after performing the given
-     * action with this CompletableFuture's result from a task running
-     * in the given executor.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied action throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> thenAcceptAsync(Consumer<? super T> block,
-                                                   Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doThenAccept(block, executor);
-    }
-
     private CompletableFuture<Void> doThenAccept(Consumer<? super T> fn,
                                                  Executor e) {
         if (fn == null) throw new NullPointerException();
@@ -1851,7 +1566,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncAccept<T>(t, fn, dst));
+                        execAsync(e, new AsyncAccept<T>(t, fn, dst));
                     else
                         fn.accept(t);
                 } catch (Throwable rex) {
@@ -1865,63 +1580,6 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when this CompletableFuture completes, after performing the given
-     * action.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied action throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> thenRun(Runnable action) {
-        return doThenRun(action, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when this CompletableFuture completes, after performing the given
-     * action from a task running in the {@link ForkJoinPool#commonPool()}.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied action throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> thenRunAsync(Runnable action) {
-        return doThenRun(action, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when this CompletableFuture completes, after performing the given
-     * action from a task running in the given executor.
-     *
-     * <p>If this CompletableFuture completes exceptionally, or the
-     * supplied action throws an exception, then the returned
-     * CompletableFuture completes exceptionally with a
-     * CompletionException holding the exception as its cause.
-     *
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> thenRunAsync(Runnable action,
-                                                Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doThenRun(action, executor);
-    }
-
     private CompletableFuture<Void> doThenRun(Runnable action,
                                               Executor e) {
         if (action == null) throw new NullPointerException();
@@ -1946,7 +1604,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncRun(action, dst));
+                        execAsync(e, new AsyncRun(action, dst));
                     else
                         action.run();
                 } catch (Throwable rex) {
@@ -1960,76 +1618,6 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when both this and the other given CompletableFuture complete,
-     * with the result of the given function of the results of the two
-     * CompletableFutures.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied function throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U,V> CompletableFuture<V> thenCombine
-        (CompletableFuture<? extends U> other,
-         BiFunction<? super T,? super U,? extends V> fn) {
-        return doThenCombine(other, fn, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when both this and the other given CompletableFuture complete,
-     * with the result of the given function of the results of the two
-     * CompletableFutures from a task running in the
-     * {@link ForkJoinPool#commonPool()}.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied function throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U,V> CompletableFuture<V> thenCombineAsync
-        (CompletableFuture<? extends U> other,
-         BiFunction<? super T,? super U,? extends V> fn) {
-        return doThenCombine(other, fn, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when both this and the other given CompletableFuture complete,
-     * with the result of the given function of the results of the two
-     * CompletableFutures from a task running in the given executor.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied function throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public <U,V> CompletableFuture<V> thenCombineAsync
-        (CompletableFuture<? extends U> other,
-         BiFunction<? super T,? super U,? extends V> fn,
-         Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doThenCombine(other, fn, executor);
-    }
-
     private <U,V> CompletableFuture<V> doThenCombine
         (CompletableFuture<? extends U> other,
          BiFunction<? super T,? super U,? extends V> fn,
@@ -2083,7 +1671,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncCombine<T,U,V>(t, u, fn, dst));
+                        execAsync(e, new AsyncCombine<T,U,V>(t, u, fn, dst));
                     else
                         v = fn.apply(t, u);
                 } catch (Throwable rex) {
@@ -2098,76 +1686,6 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when both this and the other given CompletableFuture complete,
-     * after performing the given action with the results of the two
-     * CompletableFutures.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied action throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<Void> thenAcceptBoth
-        (CompletableFuture<? extends U> other,
-         BiConsumer<? super T, ? super U> block) {
-        return doThenAcceptBoth(other, block, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when both this and the other given CompletableFuture complete,
-     * after performing the given action with the results of the two
-     * CompletableFutures from a task running in the {@link
-     * ForkJoinPool#commonPool()}.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied action throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<Void> thenAcceptBothAsync
-        (CompletableFuture<? extends U> other,
-         BiConsumer<? super T, ? super U> block) {
-        return doThenAcceptBoth(other, block, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when both this and the other given CompletableFuture complete,
-     * after performing the given action with the results of the two
-     * CompletableFutures from a task running in the given executor.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied action throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<Void> thenAcceptBothAsync
-        (CompletableFuture<? extends U> other,
-         BiConsumer<? super T, ? super U> block,
-         Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doThenAcceptBoth(other, block, executor);
-    }
-
     private <U> CompletableFuture<Void> doThenAcceptBoth
         (CompletableFuture<? extends U> other,
          BiConsumer<? super T,? super U> fn,
@@ -2220,7 +1738,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncAcceptBoth<T,U>(t, u, fn, dst));
+                        execAsync(e, new AsyncAcceptBoth<T,U>(t, u, fn, dst));
                     else
                         fn.accept(t, u);
                 } catch (Throwable rex) {
@@ -2235,71 +1753,6 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when both this and the other given CompletableFuture complete,
-     * after performing the given action.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied action throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> runAfterBoth(CompletableFuture<?> other,
-                                                Runnable action) {
-        return doRunAfterBoth(other, action, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when both this and the other given CompletableFuture complete,
-     * after performing the given action from a task running in the
-     * {@link ForkJoinPool#commonPool()}.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied action throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> runAfterBothAsync(CompletableFuture<?> other,
-                                                     Runnable action) {
-        return doRunAfterBoth(other, action, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when both this and the other given CompletableFuture complete,
-     * after performing the given action from a task running in the
-     * given executor.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, or the supplied action throws an exception,
-     * then the returned CompletableFuture completes exceptionally
-     * with a CompletionException holding the exception as its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> runAfterBothAsync(CompletableFuture<?> other,
-                                                     Runnable action,
-                                                     Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doRunAfterBoth(other, action, executor);
-    }
-
     private CompletableFuture<Void> doRunAfterBoth(CompletableFuture<?> other,
                                                    Runnable action,
                                                    Executor e) {
@@ -2338,7 +1791,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncRun(action, dst));
+                        execAsync(e, new AsyncRun(action, dst));
                     else
                         action.run();
                 } catch (Throwable rex) {
@@ -2353,89 +1806,6 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when either this or the other given CompletableFuture completes,
-     * with the result of the given function of either this or the other
-     * CompletableFuture's result.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied function
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<U> applyToEither
-        (CompletableFuture<? extends T> other,
-         Function<? super T, U> fn) {
-        return doApplyToEither(other, fn, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when either this or the other given CompletableFuture completes,
-     * with the result of the given function of either this or the other
-     * CompletableFuture's result from a task running in the
-     * {@link ForkJoinPool#commonPool()}.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied function
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<U> applyToEitherAsync
-        (CompletableFuture<? extends T> other,
-         Function<? super T, U> fn) {
-        return doApplyToEither(other, fn, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when either this or the other given CompletableFuture completes,
-     * with the result of the given function of either this or the other
-     * CompletableFuture's result from a task running in the
-     * given executor.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied function
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param fn the function to use to compute the value of
-     * the returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<U> applyToEitherAsync
-        (CompletableFuture<? extends T> other,
-         Function<? super T, U> fn,
-         Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doApplyToEither(other, fn, executor);
-    }
-
     private <U> CompletableFuture<U> doApplyToEither
         (CompletableFuture<? extends T> other,
          Function<? super T, U> fn,
@@ -2473,7 +1843,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncApply<T,U>(t, fn, dst));
+                        execAsync(e, new AsyncApply<T,U>(t, fn, dst));
                     else
                         u = fn.apply(t);
                 } catch (Throwable rex) {
@@ -2488,89 +1858,6 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when either this or the other given CompletableFuture completes,
-     * after performing the given action with the result of either this
-     * or the other CompletableFuture's result.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied action
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> acceptEither
-        (CompletableFuture<? extends T> other,
-         Consumer<? super T> block) {
-        return doAcceptEither(other, block, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when either this or the other given CompletableFuture completes,
-     * after performing the given action with the result of either this
-     * or the other CompletableFuture's result from a task running in
-     * the {@link ForkJoinPool#commonPool()}.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied action
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> acceptEitherAsync
-        (CompletableFuture<? extends T> other,
-         Consumer<? super T> block) {
-        return doAcceptEither(other, block, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when either this or the other given CompletableFuture completes,
-     * after performing the given action with the result of either this
-     * or the other CompletableFuture's result from a task running in
-     * the given executor.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied action
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param block the action to perform before completing the
-     * returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> acceptEitherAsync
-        (CompletableFuture<? extends T> other,
-         Consumer<? super T> block,
-         Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doAcceptEither(other, block, executor);
-    }
-
     private CompletableFuture<Void> doAcceptEither
         (CompletableFuture<? extends T> other,
          Consumer<? super T> fn,
@@ -2607,7 +1894,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncAccept<T>(t, fn, dst));
+                        execAsync(e, new AsyncAccept<T>(t, fn, dst));
                     else
                         fn.accept(t);
                 } catch (Throwable rex) {
@@ -2622,85 +1909,6 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed
-     * when either this or the other given CompletableFuture completes,
-     * after performing the given action.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied action
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> runAfterEither(CompletableFuture<?> other,
-                                                  Runnable action) {
-        return doRunAfterEither(other, action, null);
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when either this or the other given CompletableFuture completes,
-     * after performing the given action from a task running in the
-     * {@link ForkJoinPool#commonPool()}.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied action
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> runAfterEitherAsync
-        (CompletableFuture<?> other,
-         Runnable action) {
-        return doRunAfterEither(other, action, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a new CompletableFuture that is asynchronously completed
-     * when either this or the other given CompletableFuture completes,
-     * after performing the given action from a task running in the
-     * given executor.
-     *
-     * <p>If this and/or the other CompletableFuture complete
-     * exceptionally, then the returned CompletableFuture may also do so,
-     * with a CompletionException holding one of these exceptions as its
-     * cause.  No guarantees are made about which result or exception is
-     * used in the returned CompletableFuture.  If the supplied action
-     * throws an exception, then the returned CompletableFuture completes
-     * exceptionally with a CompletionException holding the exception as
-     * its cause.
-     *
-     * @param other the other CompletableFuture
-     * @param action the action to perform before completing the
-     * returned CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<Void> runAfterEitherAsync
-        (CompletableFuture<?> other,
-         Runnable action,
-         Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doRunAfterEither(other, action, executor);
-    }
-
     private CompletableFuture<Void> doRunAfterEither
         (CompletableFuture<?> other,
          Runnable action,
@@ -2732,7 +1940,7 @@ public class CompletableFuture<T> implements Future<T> {
             if (ex == null) {
                 try {
                     if (e != null)
-                        e.execute(new AsyncRun(action, dst));
+                        execAsync(e, new AsyncRun(action, dst));
                     else
                         action.run();
                 } catch (Throwable rex) {
@@ -2747,69 +1955,8 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a CompletableFuture that upon completion, has the same
-     * value as produced by the given function of the result of this
-     * CompletableFuture.
-     *
-     * <p>If this CompletableFuture completes exceptionally, then the
-     * returned CompletableFuture also does so, with a
-     * CompletionException holding this exception as its cause.
-     * Similarly, if the computed CompletableFuture completes
-     * exceptionally, then so does the returned CompletableFuture.
-     *
-     * @param fn the function returning a new CompletableFuture
-     * @return the CompletableFuture
-     */
-    public <U> CompletableFuture<U> thenCompose
-        (Function<? super T, CompletableFuture<U>> fn) {
-        return doThenCompose(fn, null);
-    }
-
-    /**
-     * Returns a CompletableFuture that upon completion, has the same
-     * value as that produced asynchronously using the {@link
-     * ForkJoinPool#commonPool()} by the given function of the result
-     * of this CompletableFuture.
-     *
-     * <p>If this CompletableFuture completes exceptionally, then the
-     * returned CompletableFuture also does so, with a
-     * CompletionException holding this exception as its cause.
-     * Similarly, if the computed CompletableFuture completes
-     * exceptionally, then so does the returned CompletableFuture.
-     *
-     * @param fn the function returning a new CompletableFuture
-     * @return the CompletableFuture
-     */
-    public <U> CompletableFuture<U> thenComposeAsync
-        (Function<? super T, CompletableFuture<U>> fn) {
-        return doThenCompose(fn, ForkJoinPool.commonPool());
-    }
-
-    /**
-     * Returns a CompletableFuture that upon completion, has the same
-     * value as that produced asynchronously using the given executor
-     * by the given function of this CompletableFuture.
-     *
-     * <p>If this CompletableFuture completes exceptionally, then the
-     * returned CompletableFuture also does so, with a
-     * CompletionException holding this exception as its cause.
-     * Similarly, if the computed CompletableFuture completes
-     * exceptionally, then so does the returned CompletableFuture.
-     *
-     * @param fn the function returning a new CompletableFuture
-     * @param executor the executor to use for asynchronous execution
-     * @return the CompletableFuture
-     */
-    public <U> CompletableFuture<U> thenComposeAsync
-        (Function<? super T, CompletableFuture<U>> fn,
-         Executor executor) {
-        if (executor == null) throw new NullPointerException();
-        return doThenCompose(fn, executor);
-    }
-
     private <U> CompletableFuture<U> doThenCompose
-        (Function<? super T, CompletableFuture<U>> fn,
+        (Function<? super T, ? extends CompletionStage<U>> fn,
          Executor e) {
         if (fn == null) throw new NullPointerException();
         CompletableFuture<U> dst = null;
@@ -2840,11 +1987,13 @@ public class CompletableFuture<T> implements Future<T> {
                 if (e != null) {
                     if (dst == null)
                         dst = new CompletableFuture<U>();
-                    e.execute(new AsyncCompose<T,U>(t, fn, dst));
+                    execAsync(e, new AsyncCompose<T,U>(t, fn, dst));
                 }
                 else {
                     try {
-                        if ((dst = fn.apply(t)) == null)
+                        CompletionStage<U> cs = fn.apply(t);
+                        if (cs == null ||
+                            (dst = cs.toCompletableFuture()) == null)
                             ex = new NullPointerException();
                     } catch (Throwable rex) {
                         ex = rex;
@@ -2861,28 +2010,17 @@ public class CompletableFuture<T> implements Future<T> {
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed when this
-     * CompletableFuture completes, with the result of the given
-     * function of the exception triggering this CompletableFuture's
-     * completion when it completes exceptionally; otherwise, if this
-     * CompletableFuture completes normally, then the returned
-     * CompletableFuture also completes normally with the same value.
-     *
-     * @param fn the function to use to compute the value of the
-     * returned CompletableFuture if this CompletableFuture completed
-     * exceptionally
-     * @return the new CompletableFuture
-     */
-    public CompletableFuture<T> exceptionally
-        (Function<Throwable, ? extends T> fn) {
+    private CompletableFuture<T> doWhenComplete
+        (BiConsumer<? super T, ? super Throwable> fn,
+         Executor e) {
         if (fn == null) throw new NullPointerException();
         CompletableFuture<T> dst = new CompletableFuture<T>();
-        ExceptionCompletion<T> d = null;
+        WhenCompleteCompletion<T> d = null;
         Object r;
         if ((r = result) == null) {
             CompletionNode p =
-                new CompletionNode(d = new ExceptionCompletion<T>(this, fn, dst));
+                new CompletionNode(d = new WhenCompleteCompletion<T>
+                                   (this, fn, dst, e));
             while ((r = result) == null) {
                 if (UNSAFE.compareAndSwapObject(this, COMPLETIONS,
                                                 p.next = completions, p))
@@ -2890,47 +2028,43 @@ public class CompletableFuture<T> implements Future<T> {
             }
         }
         if (r != null && (d == null || d.compareAndSet(0, 1))) {
-            T t = null; Throwable ex, dx = null;
+            T t; Throwable ex;
             if (r instanceof AltResult) {
-                if ((ex = ((AltResult)r).ex) != null) {
-                    try {
-                        t = fn.apply(ex);
-                    } catch (Throwable rex) {
-                        dx = rex;
-                    }
-                }
+                ex = ((AltResult)r).ex;
+                t = null;
             }
             else {
+                ex = null;
                 @SuppressWarnings("unchecked") T tr = (T) r;
                 t = tr;
             }
-            dst.internalComplete(t, dx);
+            Throwable dx = null;
+            try {
+                if (e != null)
+                    execAsync(e, new AsyncWhenComplete<T>(t, ex, fn, dst));
+                else
+                    fn.accept(t, ex);
+            } catch (Throwable rex) {
+                dx = rex;
+            }
+            if (e == null || dx != null)
+                dst.internalComplete(t, ex != null ? ex : dx);
         }
         helpPostComplete();
         return dst;
     }
 
-    /**
-     * Returns a new CompletableFuture that is completed when this
-     * CompletableFuture completes, with the result of the given
-     * function of the result and exception of this CompletableFuture's
-     * completion.  The given function is invoked with the result (or
-     * {@code null} if none) and the exception (or {@code null} if none)
-     * of this CompletableFuture when complete.
-     *
-     * @param fn the function to use to compute the value of the
-     * returned CompletableFuture
-     * @return the new CompletableFuture
-     */
-    public <U> CompletableFuture<U> handle
-        (BiFunction<? super T, Throwable, ? extends U> fn) {
+    private <U> CompletableFuture<U> doHandle
+        (BiFunction<? super T, Throwable, ? extends U> fn,
+         Executor e) {
         if (fn == null) throw new NullPointerException();
         CompletableFuture<U> dst = new CompletableFuture<U>();
         HandleCompletion<T,U> d = null;
         Object r;
         if ((r = result) == null) {
             CompletionNode p =
-                new CompletionNode(d = new HandleCompletion<T,U>(this, fn, dst));
+                new CompletionNode(d = new HandleCompletion<T,U>
+                                   (this, fn, dst, e));
             while ((r = result) == null) {
                 if (UNSAFE.compareAndSwapObject(this, COMPLETIONS,
                                                 p.next = completions, p))
@@ -2948,21 +2082,577 @@ public class CompletableFuture<T> implements Future<T> {
                 @SuppressWarnings("unchecked") T tr = (T) r;
                 t = tr;
             }
-            U u; Throwable dx;
+            U u = null;
+            Throwable dx = null;
             try {
-                u = fn.apply(t, ex);
-                dx = null;
+                if (e != null)
+                    execAsync(e, new AsyncCombine<T,Throwable,U>(t, ex, fn, dst));
+                else {
+                    u = fn.apply(t, ex);
+                    dx = null;
+                }
             } catch (Throwable rex) {
                 dx = rex;
                 u = null;
             }
-            dst.internalComplete(u, dx);
+            if (e == null || dx != null)
+                dst.internalComplete(u, dx);
         }
         helpPostComplete();
         return dst;
     }
 
 
+    // public methods
+
+    /**
+     * Creates a new incomplete CompletableFuture.
+     */
+    public CompletableFuture() {
+    }
+
+    /**
+     * Returns a new CompletableFuture that is asynchronously completed
+     * by a task running in the {@link ForkJoinPool#commonPool()} with
+     * the value obtained by calling the given Supplier.
+     *
+     * @param supplier a function returning the value to be used
+     * to complete the returned CompletableFuture
+     * @param <U> the function's return type
+     * @return the new CompletableFuture
+     */
+    public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier) {
+        if (supplier == null) throw new NullPointerException();
+        CompletableFuture<U> f = new CompletableFuture<U>();
+        execAsync(ForkJoinPool.commonPool(), new AsyncSupply<U>(supplier, f));
+        return f;
+    }
+
+    /**
+     * Returns a new CompletableFuture that is asynchronously completed
+     * by a task running in the given executor with the value obtained
+     * by calling the given Supplier.
+     *
+     * @param supplier a function returning the value to be used
+     * to complete the returned CompletableFuture
+     * @param executor the executor to use for asynchronous execution
+     * @param <U> the function's return type
+     * @return the new CompletableFuture
+     */
+    public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier,
+                                                       Executor executor) {
+        if (executor == null || supplier == null)
+            throw new NullPointerException();
+        CompletableFuture<U> f = new CompletableFuture<U>();
+        execAsync(executor, new AsyncSupply<U>(supplier, f));
+        return f;
+    }
+
+    /**
+     * Returns a new CompletableFuture that is asynchronously completed
+     * by a task running in the {@link ForkJoinPool#commonPool()} after
+     * it runs the given action.
+     *
+     * @param runnable the action to run before completing the
+     * returned CompletableFuture
+     * @return the new CompletableFuture
+     */
+    public static CompletableFuture<Void> runAsync(Runnable runnable) {
+        if (runnable == null) throw new NullPointerException();
+        CompletableFuture<Void> f = new CompletableFuture<Void>();
+        execAsync(ForkJoinPool.commonPool(), new AsyncRun(runnable, f));
+        return f;
+    }
+
+    /**
+     * Returns a new CompletableFuture that is asynchronously completed
+     * by a task running in the given executor after it runs the given
+     * action.
+     *
+     * @param runnable the action to run before completing the
+     * returned CompletableFuture
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletableFuture
+     */
+    public static CompletableFuture<Void> runAsync(Runnable runnable,
+                                                   Executor executor) {
+        if (executor == null || runnable == null)
+            throw new NullPointerException();
+        CompletableFuture<Void> f = new CompletableFuture<Void>();
+        execAsync(executor, new AsyncRun(runnable, f));
+        return f;
+    }
+
+    /**
+     * Returns a new CompletableFuture that is already completed with
+     * the given value.
+     *
+     * @param value the value
+     * @param <U> the type of the value
+     * @return the completed CompletableFuture
+     */
+    public static <U> CompletableFuture<U> completedFuture(U value) {
+        CompletableFuture<U> f = new CompletableFuture<U>();
+        f.result = (value == null) ? NIL : value;
+        return f;
+    }
+
+    /**
+     * Returns {@code true} if completed in any fashion: normally,
+     * exceptionally, or via cancellation.
+     *
+     * @return {@code true} if completed
+     */
+    public boolean isDone() {
+        return result != null;
+    }
+
+    /**
+     * Waits if necessary for this future to complete, and then
+     * returns its result.
+     *
+     * @return the result value
+     * @throws CancellationException if this future was cancelled
+     * @throws ExecutionException if this future completed exceptionally
+     * @throws InterruptedException if the current thread was interrupted
+     * while waiting
+     */
+    public T get() throws InterruptedException, ExecutionException {
+        Object r; Throwable ex, cause;
+        if ((r = result) == null && (r = waitingGet(true)) == null)
+            throw new InterruptedException();
+        if (!(r instanceof AltResult)) {
+            @SuppressWarnings("unchecked") T tr = (T) r;
+            return tr;
+        }
+        if ((ex = ((AltResult)r).ex) == null)
+            return null;
+        if (ex instanceof CancellationException)
+            throw (CancellationException)ex;
+        if ((ex instanceof CompletionException) &&
+            (cause = ex.getCause()) != null)
+            ex = cause;
+        throw new ExecutionException(ex);
+    }
+
+    /**
+     * Waits if necessary for at most the given time for this future
+     * to complete, and then returns its result, if available.
+     *
+     * @param timeout the maximum time to wait
+     * @param unit the time unit of the timeout argument
+     * @return the result value
+     * @throws CancellationException if this future was cancelled
+     * @throws ExecutionException if this future completed exceptionally
+     * @throws InterruptedException if the current thread was interrupted
+     * while waiting
+     * @throws TimeoutException if the wait timed out
+     */
+    public T get(long timeout, TimeUnit unit)
+        throws InterruptedException, ExecutionException, TimeoutException {
+        Object r; Throwable ex, cause;
+        long nanos = unit.toNanos(timeout);
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        if ((r = result) == null)
+            r = timedAwaitDone(nanos);
+        if (!(r instanceof AltResult)) {
+            @SuppressWarnings("unchecked") T tr = (T) r;
+            return tr;
+        }
+        if ((ex = ((AltResult)r).ex) == null)
+            return null;
+        if (ex instanceof CancellationException)
+            throw (CancellationException)ex;
+        if ((ex instanceof CompletionException) &&
+            (cause = ex.getCause()) != null)
+            ex = cause;
+        throw new ExecutionException(ex);
+    }
+
+    /**
+     * Returns the result value when complete, or throws an
+     * (unchecked) exception if completed exceptionally. To better
+     * conform with the use of common functional forms, if a
+     * computation involved in the completion of this
+     * CompletableFuture threw an exception, this method throws an
+     * (unchecked) {@link CompletionException} with the underlying
+     * exception as its cause.
+     *
+     * @return the result value
+     * @throws CancellationException if the computation was cancelled
+     * @throws CompletionException if this future completed
+     * exceptionally or a completion computation threw an exception
+     */
+    public T join() {
+        Object r; Throwable ex;
+        if ((r = result) == null)
+            r = waitingGet(false);
+        if (!(r instanceof AltResult)) {
+            @SuppressWarnings("unchecked") T tr = (T) r;
+            return tr;
+        }
+        if ((ex = ((AltResult)r).ex) == null)
+            return null;
+        if (ex instanceof CancellationException)
+            throw (CancellationException)ex;
+        if (ex instanceof CompletionException)
+            throw (CompletionException)ex;
+        throw new CompletionException(ex);
+    }
+
+    /**
+     * Returns the result value (or throws any encountered exception)
+     * if completed, else returns the given valueIfAbsent.
+     *
+     * @param valueIfAbsent the value to return if not completed
+     * @return the result value, if completed, else the given valueIfAbsent
+     * @throws CancellationException if the computation was cancelled
+     * @throws CompletionException if this future completed
+     * exceptionally or a completion computation threw an exception
+     */
+    public T getNow(T valueIfAbsent) {
+        Object r; Throwable ex;
+        if ((r = result) == null)
+            return valueIfAbsent;
+        if (!(r instanceof AltResult)) {
+            @SuppressWarnings("unchecked") T tr = (T) r;
+            return tr;
+        }
+        if ((ex = ((AltResult)r).ex) == null)
+            return null;
+        if (ex instanceof CancellationException)
+            throw (CancellationException)ex;
+        if (ex instanceof CompletionException)
+            throw (CompletionException)ex;
+        throw new CompletionException(ex);
+    }
+
+    /**
+     * If not already completed, sets the value returned by {@link
+     * #get()} and related methods to the given value.
+     *
+     * @param value the result value
+     * @return {@code true} if this invocation caused this CompletableFuture
+     * to transition to a completed state, else {@code false}
+     */
+    public boolean complete(T value) {
+        boolean triggered = result == null &&
+            UNSAFE.compareAndSwapObject(this, RESULT, null,
+                                        value == null ? NIL : value);
+        postComplete();
+        return triggered;
+    }
+
+    /**
+     * If not already completed, causes invocations of {@link #get()}
+     * and related methods to throw the given exception.
+     *
+     * @param ex the exception
+     * @return {@code true} if this invocation caused this CompletableFuture
+     * to transition to a completed state, else {@code false}
+     */
+    public boolean completeExceptionally(Throwable ex) {
+        if (ex == null) throw new NullPointerException();
+        boolean triggered = result == null &&
+            UNSAFE.compareAndSwapObject(this, RESULT, null, new AltResult(ex));
+        postComplete();
+        return triggered;
+    }
+
+    // CompletionStage methods
+
+    public <U> CompletableFuture<U> thenApply
+        (Function<? super T,? extends U> fn) {
+        return doThenApply(fn, null);
+    }
+
+    public <U> CompletableFuture<U> thenApplyAsync
+        (Function<? super T,? extends U> fn) {
+        return doThenApply(fn, ForkJoinPool.commonPool());
+    }
+
+    public <U> CompletableFuture<U> thenApplyAsync
+        (Function<? super T,? extends U> fn,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doThenApply(fn, executor);
+    }
+
+    public CompletableFuture<Void> thenAccept
+        (Consumer<? super T> action) {
+        return doThenAccept(action, null);
+    }
+
+    public CompletableFuture<Void> thenAcceptAsync
+        (Consumer<? super T> action) {
+        return doThenAccept(action, ForkJoinPool.commonPool());
+    }
+
+    public CompletableFuture<Void> thenAcceptAsync
+        (Consumer<? super T> action,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doThenAccept(action, executor);
+    }
+
+    public CompletableFuture<Void> thenRun
+        (Runnable action) {
+        return doThenRun(action, null);
+    }
+
+    public CompletableFuture<Void> thenRunAsync
+        (Runnable action) {
+        return doThenRun(action, ForkJoinPool.commonPool());
+    }
+
+    public CompletableFuture<Void> thenRunAsync
+        (Runnable action,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doThenRun(action, executor);
+    }
+
+    public <U,V> CompletableFuture<V> thenCombine
+        (CompletionStage<? extends U> other,
+         BiFunction<? super T,? super U,? extends V> fn) {
+        return doThenCombine(other.toCompletableFuture(), fn, null);
+    }
+
+    public <U,V> CompletableFuture<V> thenCombineAsync
+        (CompletionStage<? extends U> other,
+         BiFunction<? super T,? super U,? extends V> fn) {
+        return doThenCombine(other.toCompletableFuture(), fn,
+                             ForkJoinPool.commonPool());
+    }
+
+    public <U,V> CompletableFuture<V> thenCombineAsync
+        (CompletionStage<? extends U> other,
+         BiFunction<? super T,? super U,? extends V> fn,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doThenCombine(other.toCompletableFuture(), fn, executor);
+    }
+
+    public <U> CompletableFuture<Void> thenAcceptBoth
+        (CompletionStage<? extends U> other,
+         BiConsumer<? super T, ? super U> action) {
+        return doThenAcceptBoth(other.toCompletableFuture(), action, null);
+    }
+
+    public <U> CompletableFuture<Void> thenAcceptBothAsync
+        (CompletionStage<? extends U> other,
+         BiConsumer<? super T, ? super U> action) {
+        return doThenAcceptBoth(other.toCompletableFuture(), action,
+                                ForkJoinPool.commonPool());
+    }
+
+    public <U> CompletableFuture<Void> thenAcceptBothAsync
+        (CompletionStage<? extends U> other,
+         BiConsumer<? super T, ? super U> action,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doThenAcceptBoth(other.toCompletableFuture(), action, executor);
+    }
+
+    public CompletableFuture<Void> runAfterBoth
+        (CompletionStage<?> other,
+         Runnable action) {
+        return doRunAfterBoth(other.toCompletableFuture(), action, null);
+    }
+
+    public CompletableFuture<Void> runAfterBothAsync
+        (CompletionStage<?> other,
+         Runnable action) {
+        return doRunAfterBoth(other.toCompletableFuture(), action,
+                              ForkJoinPool.commonPool());
+    }
+
+    public CompletableFuture<Void> runAfterBothAsync
+        (CompletionStage<?> other,
+         Runnable action,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doRunAfterBoth(other.toCompletableFuture(), action, executor);
+    }
+
+
+    public <U> CompletableFuture<U> applyToEither
+        (CompletionStage<? extends T> other,
+         Function<? super T, U> fn) {
+        return doApplyToEither(other.toCompletableFuture(), fn, null);
+    }
+
+    public <U> CompletableFuture<U> applyToEitherAsync
+        (CompletionStage<? extends T> other,
+         Function<? super T, U> fn) {
+        return doApplyToEither(other.toCompletableFuture(), fn,
+                               ForkJoinPool.commonPool());
+    }
+
+    public <U> CompletableFuture<U> applyToEitherAsync
+        (CompletionStage<? extends T> other,
+         Function<? super T, U> fn,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doApplyToEither(other.toCompletableFuture(), fn, executor);
+    }
+
+    public CompletableFuture<Void> acceptEither
+        (CompletionStage<? extends T> other,
+         Consumer<? super T> action) {
+        return doAcceptEither(other.toCompletableFuture(), action, null);
+    }
+
+    public CompletableFuture<Void> acceptEitherAsync
+        (CompletionStage<? extends T> other,
+         Consumer<? super T> action) {
+        return doAcceptEither(other.toCompletableFuture(), action,
+                              ForkJoinPool.commonPool());
+    }
+
+    public CompletableFuture<Void> acceptEitherAsync
+        (CompletionStage<? extends T> other,
+         Consumer<? super T> action,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doAcceptEither(other.toCompletableFuture(), action, executor);
+    }
+
+    public CompletableFuture<Void> runAfterEither(CompletionStage<?> other,
+                                                  Runnable action) {
+        return doRunAfterEither(other.toCompletableFuture(), action, null);
+    }
+
+    public CompletableFuture<Void> runAfterEitherAsync
+        (CompletionStage<?> other,
+         Runnable action) {
+        return doRunAfterEither(other.toCompletableFuture(), action,
+                                ForkJoinPool.commonPool());
+    }
+
+    public CompletableFuture<Void> runAfterEitherAsync
+        (CompletionStage<?> other,
+         Runnable action,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doRunAfterEither(other.toCompletableFuture(), action, executor);
+    }
+
+    public <U> CompletableFuture<U> thenCompose
+        (Function<? super T, ? extends CompletionStage<U>> fn) {
+        return doThenCompose(fn, null);
+    }
+
+    public <U> CompletableFuture<U> thenComposeAsync
+        (Function<? super T, ? extends CompletionStage<U>> fn) {
+        return doThenCompose(fn, ForkJoinPool.commonPool());
+    }
+
+    public <U> CompletableFuture<U> thenComposeAsync
+        (Function<? super T, ? extends CompletionStage<U>> fn,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doThenCompose(fn, executor);
+    }
+
+    public CompletableFuture<T> whenComplete
+        (BiConsumer<? super T, ? super Throwable> action) {
+        return doWhenComplete(action, null);
+    }
+
+    public CompletableFuture<T> whenCompleteAsync
+        (BiConsumer<? super T, ? super Throwable> action) {
+        return doWhenComplete(action, ForkJoinPool.commonPool());
+    }
+
+    public CompletableFuture<T> whenCompleteAsync
+        (BiConsumer<? super T, ? super Throwable> action,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doWhenComplete(action, executor);
+    }
+
+    public <U> CompletableFuture<U> handle
+        (BiFunction<? super T, Throwable, ? extends U> fn) {
+        return doHandle(fn, null);
+    }
+
+    public <U> CompletableFuture<U> handleAsync
+        (BiFunction<? super T, Throwable, ? extends U> fn) {
+        return doHandle(fn, ForkJoinPool.commonPool());
+    }
+
+    public <U> CompletableFuture<U> handleAsync
+        (BiFunction<? super T, Throwable, ? extends U> fn,
+         Executor executor) {
+        if (executor == null) throw new NullPointerException();
+        return doHandle(fn, executor);
+    }
+
+    /**
+     * Returns this CompletableFuture
+     *
+     * @return this CompletableFuture
+     */
+    public CompletableFuture<T> toCompletableFuture() {
+        return this;
+    }
+
+    // not in interface CompletionStage
+
+    /**
+     * Returns a new CompletableFuture that is completed when this
+     * CompletableFuture completes, with the result of the given
+     * function of the exception triggering this CompletableFuture's
+     * completion when it completes exceptionally; otherwise, if this
+     * CompletableFuture completes normally, then the returned
+     * CompletableFuture also completes normally with the same value.
+     * Note: More flexible versions of this functionality are
+     * available using methods {@code whenComplete} and {@code handle}.
+     *
+     * @param fn the function to use to compute the value of the
+     * returned CompletableFuture if this CompletableFuture completed
+     * exceptionally
+     * @return the new CompletableFuture
+     */
+    public CompletableFuture<T> exceptionally
+        (Function<Throwable, ? extends T> fn) {
+        if (fn == null) throw new NullPointerException();
+        CompletableFuture<T> dst = new CompletableFuture<T>();
+        ExceptionCompletion<T> d = null;
+        Object r;
+        if ((r = result) == null) {
+            CompletionNode p =
+                new CompletionNode(d = new ExceptionCompletion<T>
+                                   (this, fn, dst));
+            while ((r = result) == null) {
+                if (UNSAFE.compareAndSwapObject(this, COMPLETIONS,
+                                                p.next = completions, p))
+                    break;
+            }
+        }
+        if (r != null && (d == null || d.compareAndSet(0, 1))) {
+            T t = null; Throwable ex, dx = null;
+            if (r instanceof AltResult) {
+                if ((ex = ((AltResult)r).ex) != null) {
+                    try {
+                        t = fn.apply(ex);
+                    } catch (Throwable rex) {
+                        dx = rex;
+                    }
+                }
+            }
+            else {
+                @SuppressWarnings("unchecked") T tr = (T) r;
+                t = tr;
+            }
+            dst.internalComplete(t, dx);
+        }
+        helpPostComplete();
+        return dst;
+    }
+
     /* ------------- Arbitrary-arity constructions -------------- */
 
     /*
@@ -3215,6 +2905,21 @@ public class CompletableFuture<T> implements Future<T> {
     }
 
     /**
+     * Returns {@code true} if this CompletableFuture completed
+     * exceptionally, in any way. Possible causes include
+     * cancellation, explicit invocation of {@code
+     * completeExceptionally}, and abrupt termination of a
+     * CompletionStage action.
+     *
+     * @return {@code true} if this CompletableFuture completed
+     * exceptionally
+     */
+    public boolean isCompletedExceptionally() {
+        Object r;
+        return ((r = result) instanceof AltResult) && r != NIL;
+    }
+
+    /**
      * Forcibly sets or resets the value subsequently returned by
      * method {@link #get()} and related methods, whether or not
      * already completed. This method is designed for use only in
diff --git a/src/share/classes/java/util/concurrent/CompletionStage.java b/src/share/classes/java/util/concurrent/CompletionStage.java
new file mode 100644
index 0000000000..6de60980cf
--- /dev/null
+++ b/src/share/classes/java/util/concurrent/CompletionStage.java
@@ -0,0 +1,760 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent;
+import java.util.function.Supplier;
+import java.util.function.Consumer;
+import java.util.function.BiConsumer;
+import java.util.function.Function;
+import java.util.function.BiFunction;
+import java.util.concurrent.Executor;
+
+/**
+ * A stage of a possibly asynchronous computation, that performs an
+ * action or computes a value when another CompletionStage completes.
+ * A stage completes upon termination of its computation, but this may
+ * in turn trigger other dependent stages.  The functionality defined
+ * in this interface takes only a few basic forms, which expand out to
+ * a larger set of methods to capture a range of usage styles: <ul>
+ *
+ * <li>The computation performed by a stage may be expressed as a
+ * Function, Consumer, or Runnable (using methods with names including
+ * <em>apply</em>, <em>accept</em>, or <em>run</em>, respectively)
+ * depending on whether it requires arguments and/or produces results.
+ * For example, {@code stage.thenApply(x -> square(x)).thenAccept(x ->
+ * System.out.print(x)).thenRun(() -> System.out.println())}. An
+ * additional form (<em>compose</em>) applies functions of stages
+ * themselves, rather than their results. </li>
+ *
+ * <li> One stage's execution may be triggered by completion of a
+ * single stage, or both of two stages, or either of two stages.
+ * Dependencies on a single stage are arranged using methods with
+ * prefix <em>then</em>. Those triggered by completion of
+ * <em>both</em> of two stages may <em>combine</em> their results or
+ * effects, using correspondingly named methods. Those triggered by
+ * <em>either</em> of two stages make no guarantees about which of the
+ * results or effects are used for the dependent stage's
+ * computation.</li>
+ *
+ * <li> Dependencies among stages control the triggering of
+ * computations, but do not otherwise guarantee any particular
+ * ordering. Additionally, execution of a new stage's computations may
+ * be arranged in any of three ways: default execution, default
+ * asynchronous execution (using methods with suffix <em>async</em>
+ * that employ the stage's default asynchronous execution facility),
+ * or custom (via a supplied {@link Executor}).  The execution
+ * properties of default and async modes are specified by
+ * CompletionStage implementations, not this interface. Methods with
+ * explicit Executor arguments may have arbitrary execution
+ * properties, and might not even support concurrent execution, but
+ * are arranged for processing in a way that accommodates asynchrony.
+ *
+ * <li> Two method forms support processing whether the triggering
+ * stage completed normally or exceptionally: Method {@link
+ * #whenComplete whenComplete} allows injection of an action
+ * regardless of outcome, otherwise preserving the outcome in its
+ * completion. Method {@link #handle handle} additionally allows the
+ * stage to compute a replacement result that may enable further
+ * processing by other dependent stages.  In all other cases, if a
+ * stage's computation terminates abruptly with an (unchecked)
+ * exception or error, then all dependent stages requiring its
+ * completion complete exceptionally as well, with a {@link
+ * CompletionException} holding the exception as its cause.  If a
+ * stage is dependent on <em>both</em> of two stages, and both
+ * complete exceptionally, then the CompletionException may correspond
+ * to either one of these exceptions.  If a stage is dependent on
+ * <em>either</em> of two others, and only one of them completes
+ * exceptionally, no guarantees are made about whether the dependent
+ * stage completes normally or exceptionally. In the case of method
+ * {@code whenComplete}, when the supplied action itself encounters an
+ * exception, then the stage exceptionally completes with this
+ * exception if not already completed exceptionally.</li>
+ *
+ * </ul>
+ *
+ * <p>All methods adhere to the above triggering, execution, and
+ * exceptional completion specifications (which are not repeated in
+ * individual method specifications). Additionally, while arguments
+ * used to pass a completion result (that is, for parameters of type
+ * {@code T}) for methods accepting them may be null, passing a null
+ * value for any other parameter will result in a {@link
+ * NullPointerException} being thrown.
+ *
+ * <p>This interface does not define methods for initially creating,
+ * forcibly completing normally or exceptionally, probing completion
+ * status or results, or awaiting completion of a stage.
+ * Implementations of CompletionStage may provide means of achieving
+ * such effects, as appropriate.  Method {@link #toCompletableFuture}
+ * enables interoperability among different implementations of this
+ * interface by providing a common conversion type.
+ *
+ * @author Doug Lea
+ * @since 1.8
+ */
+public interface CompletionStage<T> {
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed with this stage's result as the argument
+     * to the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> thenApply(Function<? super T,? extends U> fn);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed using this stage's default asynchronous
+     * execution facility, with this stage's result as the argument to
+     * the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> thenApplyAsync
+        (Function<? super T,? extends U> fn);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed using the supplied Executor, with this
+     * stage's result as the argument to the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> thenApplyAsync
+        (Function<? super T,? extends U> fn,
+         Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed with this stage's result as the argument
+     * to the supplied action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> thenAccept(Consumer<? super T> action);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed using this stage's default asynchronous
+     * execution facility, with this stage's result as the argument to
+     * the supplied action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed using the supplied Executor, with this
+     * stage's result as the argument to the supplied action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> thenAcceptAsync(Consumer<? super T> action,
+                                                 Executor executor);
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, executes the given action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> thenRun(Runnable action);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, executes the given action using this stage's default
+     * asynchronous execution facility.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> thenRunAsync(Runnable action);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, executes the given action using the supplied Executor.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> thenRunAsync(Runnable action,
+                                              Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage both complete normally, is executed with the two
+     * results as arguments to the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param <U> the type of the other CompletionStage's result
+     * @param <V> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U,V> CompletionStage<V> thenCombine
+        (CompletionStage<? extends U> other,
+         BiFunction<? super T,? super U,? extends V> fn);
+
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage complete normally, is executed using this stage's
+     * default asynchronous execution facility, with the two results
+     * as arguments to the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param <U> the type of the other CompletionStage's result
+     * @param <V> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U,V> CompletionStage<V> thenCombineAsync
+        (CompletionStage<? extends U> other,
+         BiFunction<? super T,? super U,? extends V> fn);
+
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage complete normally, is executed using the supplied
+     * executor, with the two results as arguments to the supplied
+     * function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @param <U> the type of the other CompletionStage's result
+     * @param <V> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U,V> CompletionStage<V> thenCombineAsync
+        (CompletionStage<? extends U> other,
+         BiFunction<? super T,? super U,? extends V> fn,
+         Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage both complete normally, is executed with the two
+     * results as arguments to the supplied action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @param <U> the type of the other CompletionStage's result
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<Void> thenAcceptBoth
+        (CompletionStage<? extends U> other,
+         BiConsumer<? super T, ? super U> action);
+
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage complete normally, is executed using this stage's
+     * default asynchronous execution facility, with the two results
+     * as arguments to the supplied action.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @param <U> the type of the other CompletionStage's result
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<Void> thenAcceptBothAsync
+        (CompletionStage<? extends U> other,
+         BiConsumer<? super T, ? super U> action);
+
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage complete normally, is executed using the supplied
+     * executor, with the two results as arguments to the supplied
+     * function.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @param <U> the type of the other CompletionStage's result
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<Void> thenAcceptBothAsync
+        (CompletionStage<? extends U> other,
+         BiConsumer<? super T, ? super U> action,
+         Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage both complete normally, executes the given action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> runAfterBoth(CompletionStage<?> other,
+                                              Runnable action);
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage complete normally, executes the given action using
+     * this stage's default asynchronous execution facility.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,
+                                                   Runnable action);
+
+    /**
+     * Returns a new CompletionStage that, when this and the other
+     * given stage complete normally, executes the given action using
+     * the supplied executor
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> runAfterBothAsync(CompletionStage<?> other,
+                                                   Runnable action,
+                                                   Executor executor);
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, is executed with the
+     * corresponding result as argument to the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> applyToEither
+        (CompletionStage<? extends T> other,
+         Function<? super T, U> fn);
+
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, is executed using this
+     * stage's default asynchronous execution facility, with the
+     * corresponding result as argument to the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> applyToEitherAsync
+        (CompletionStage<? extends T> other,
+         Function<? super T, U> fn);
+
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, is executed using the
+     * supplied executor, with the corresponding result as argument to
+     * the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param fn the function to use to compute the value of
+     * the returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> applyToEitherAsync
+        (CompletionStage<? extends T> other,
+         Function<? super T, U> fn,
+         Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, is executed with the
+     * corresponding result as argument to the supplied action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> acceptEither
+        (CompletionStage<? extends T> other,
+         Consumer<? super T> action);
+
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, is executed using this
+     * stage's default asynchronous execution facility, with the
+     * corresponding result as argument to the supplied action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> acceptEitherAsync
+        (CompletionStage<? extends T> other,
+         Consumer<? super T> action);
+
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, is executed using the
+     * supplied executor, with the corresponding result as argument to
+     * the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> acceptEitherAsync
+        (CompletionStage<? extends T> other,
+         Consumer<? super T> action,
+         Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, executes the given action.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> runAfterEither(CompletionStage<?> other,
+                                                Runnable action);
+
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, executes the given action
+     * using this stage's default asynchronous execution facility.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> runAfterEitherAsync
+        (CompletionStage<?> other,
+         Runnable action);
+
+    /**
+     * Returns a new CompletionStage that, when either this or the
+     * other given stage complete normally, executes the given action
+     * using supplied executor.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param other the other CompletionStage
+     * @param action the action to perform before completing the
+     * returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletionStage
+     */
+    public CompletionStage<Void> runAfterEitherAsync
+        (CompletionStage<?> other,
+         Runnable action,
+         Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed with this stage as the argument
+     * to the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param fn the function returning a new CompletionStage
+     * @param <U> the type of the returned CompletionStage's result
+     * @return the CompletionStage
+     */
+    public <U> CompletionStage<U> thenCompose
+        (Function<? super T, ? extends CompletionStage<U>> fn);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed using this stage's default asynchronous
+     * execution facility, with this stage as the argument to the
+     * supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param fn the function returning a new CompletionStage
+     * @param <U> the type of the returned CompletionStage's result
+     * @return the CompletionStage
+     */
+    public <U> CompletionStage<U> thenComposeAsync
+        (Function<? super T, ? extends CompletionStage<U>> fn);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * normally, is executed using the supplied Executor, with this
+     * stage's result as the argument to the supplied function.
+     *
+     * See the {@link CompletionStage} documentation for rules
+     * covering exceptional completion.
+     *
+     * @param fn the function returning a new CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @param <U> the type of the returned CompletionStage's result
+     * @return the CompletionStage
+     */
+    public <U> CompletionStage<U> thenComposeAsync
+        (Function<? super T, ? extends CompletionStage<U>> fn,
+         Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * exceptionally, is executed with this stage's exception as the
+     * argument to the supplied function.  Otherwise, if this stage
+     * completes normally, then the returned stage also completes
+     * normally with the same value.
+     *
+     * @param fn the function to use to compute the value of the
+     * returned CompletionStage if this CompletionStage completed
+     * exceptionally
+     * @return the new CompletionStage
+     */
+    public CompletionStage<T> exceptionally
+        (Function<Throwable, ? extends T> fn);
+
+    /**
+     * Returns a new CompletionStage with the same result or exception
+     * as this stage, and when this stage completes, executes the
+     * given action with the result (or {@code null} if none) and the
+     * exception (or {@code null} if none) of this stage.
+     *
+     * @param action the action to perform
+     * @return the new CompletionStage
+     */
+    public CompletionStage<T> whenComplete
+        (BiConsumer<? super T, ? super Throwable> action);
+
+    /**
+     * Returns a new CompletionStage with the same result or exception
+     * as this stage, and when this stage completes, executes the
+     * given action executes the given action using this stage's
+     * default asynchronous execution facility, with the result (or
+     * {@code null} if none) and the exception (or {@code null} if
+     * none) of this stage as arguments.
+     *
+     * @param action the action to perform
+     * @return the new CompletionStage
+     */
+    public CompletionStage<T> whenCompleteAsync
+        (BiConsumer<? super T, ? super Throwable> action);
+
+    /**
+     * Returns a new CompletionStage with the same result or exception
+     * as this stage, and when this stage completes, executes using
+     * the supplied Executor, the given action with the result (or
+     * {@code null} if none) and the exception (or {@code null} if
+     * none) of this stage as arguments.
+     *
+     * @param action the action to perform
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletionStage
+     */
+    public CompletionStage<T> whenCompleteAsync
+        (BiConsumer<? super T, ? super Throwable> action,
+         Executor executor);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * either normally or exceptionally, is executed with this stage's
+     * result and exception as arguments to the supplied function.
+     * The given function is invoked with the result (or {@code null}
+     * if none) and the exception (or {@code null} if none) of this
+     * stage when complete as arguments.
+     *
+     * @param fn the function to use to compute the value of the
+     * returned CompletionStage
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> handle
+        (BiFunction<? super T, Throwable, ? extends U> fn);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * either normally or exceptionally, is executed using this stage's
+     * default asynchronous execution facility, with this stage's
+     * result and exception as arguments to the supplied function.
+     * The given function is invoked with the result (or {@code null}
+     * if none) and the exception (or {@code null} if none) of this
+     * stage when complete as arguments.
+     *
+     * @param fn the function to use to compute the value of the
+     * returned CompletionStage
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> handleAsync
+        (BiFunction<? super T, Throwable, ? extends U> fn);
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * either normally or exceptionally, is executed using the
+     * supplied executor, with this stage's result and exception as
+     * arguments to the supplied function.  The given function is
+     * invoked with the result (or {@code null} if none) and the
+     * exception (or {@code null} if none) of this stage when complete
+     * as arguments.
+     *
+     * @param fn the function to use to compute the value of the
+     * returned CompletionStage
+     * @param executor the executor to use for asynchronous execution
+     * @param <U> the function's return type
+     * @return the new CompletionStage
+     */
+    public <U> CompletionStage<U> handleAsync
+        (BiFunction<? super T, Throwable, ? extends U> fn,
+         Executor executor);
+
+    /**
+     * Returns a {@link CompletableFuture} maintaining the same
+     * completion properties as this stage. If this stage is already a
+     * CompletableFuture, this method may return this stage itself.
+     * Otherwise, invocation of this method may be equivalent in
+     * effect to {@code thenApply(x -> x)}, but returning an instance
+     * of type {@code CompletableFuture}. A CompletionStage
+     * implementation that does not choose to interoperate with others
+     * may throw {@code UnsupportedOperationException}.
+     *
+     * @return the CompletableFuture
+     * @throws UnsupportedOperationException if this implementation
+     * does not interoperate with CompletableFuture
+     */
+    public CompletableFuture<T> toCompletableFuture();
+
+}